1. Field of the Invention
The present invention relates to solid state lasers, and more particularly to praseodymium based solid state lasers operating at wavelengths of 1.6, 2.4, 5, and 7 .mu.m.
2. Description of the Related Art
Efficient solid state lasers are desired for a number of applications, including point-to-point communications, illuminators for IR imaging systems, and remote chemical and biological sensing. Solid state lasers offer advantages over liquid and gas lasers in durability and compactness. In particular, solid state lasers operating at wavelengths of about 1.6 .mu.m, about 2.4 .mu.m, about 5 .mu.m, and about 7 .mu.m are desired.
Efficient mid-IR rare earth lasers have not been developed. The principal difficulty in making such lasers has been multiple phonon quenching. In this process, the electronic energy of a rare earth ion is transferred to the vibration modes of the host material lattice (phonons). This reduces the useful time for which the rare earth can store energy. The maximum phonon energy of a particular host (typically expressed in units of cm.sup.-1) is a material property, and can be measured by, e.g., Raman spectroscopy.
As the energy of a laser transition decreases (i.e., as the wavelength increases), the multiple phonon quenching rates typically increase rapidly. For a desired laser with a transition energy that is less than five times the maximum phonon energy for a given host, the quenching rates will be unacceptably high for efficient laser operation.